1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to a brushless motor for driving an inner tub or a pulsator in a washing machine.
2. Background of the Related Art
In general, the washing machine washes contaminated laundry clean by driving the inner tub or the pulsator by using a motor to circulate washing water having detergent contained therein. FIG. 1 illustrates key parts of a related art full automatic washing machine, provided with an inner tub 1, an outer tub 2, and a shaft 5 having one end connected both to the pulsator 3 fitted inside of the inner tub 1 and the inner tub 1 and the other end having serration 5a connected to a brushless motor 4. The brushless motor 4 designed to make regular and reverse rotation for driving the inner tub 1 and the pulsator 3 has a structure as shown in FIGS. 2 and 3.
That is, referring to FIG. 2, the brushless motor 4 is provided with a stator 10 having a coil 12 fitted to an upper frame 11 having a bearing 6 therein which is in turn fitted to the outer tub 2, and a rotor 20 having a lower frame 21 fitted to an outer circumference of the stator for being rotated by a polarity difference. As shown in FIG. 3, there are a plurality of magnets 22 fitted along an inside circumference of the lower frame 21 in the rotor 20 at fixed intervals, and a back yoke 23 between the magnets and the lower frame for forming a magnetic path and supporting the magnets. There are a plurality of draft holes 24 in a bottom surface of the lower frame. And, there is a support member 30 having female serration 31 along an inside surface injection molded as a unit with, or bonded to the lower frame 21 for transmission of a rotating power from the rotor to the shaft 5 having the male serration and maintaining a gap between the upper frame 11 and the lower frame 21.
The operation of the aforementioned system will be explained.
Upon application of a power to the brushless motor 4, the rotor 20 of the motor rotates in one direction by a polarity difference from the stator 10 and a flow of magnetic flux along the back yoke 23, to rotate the support member 30 coupled to the lower frame 21 of the rotor 20. According to this, the shaft 5 coupled with the female serration 31 inside of the support member 30 receives the rotating force of the rotor 20 through the support member 30 to rotate the inner tub 1 coupled to the shaft 5, thereby facilitating washing of the laundry.
However, the related art brushless motor has the following various problems caused by the structure.
First, the general plastic injection molded lower frame 21 in the rotor 20 of the related art brushless motor 4 impedes smooth dissipation of a heat generated during operation of the motor 4 to keep accumulation of the heat inside of the motor 4, that causes thermal distortion of the lower frame 21 and various components, and degrades the performance rapidly and shortens a lifetime of the motor. Moreover, the many steps required for injection molding of the rotor 20 in fabrication of the brushless motor 4 takes much time period, which drops a productivity, and the reinforcement required for the rotor 20 increases a total weight.
Second, the requirement for a separate device, such as a jig(not shown), for fitting the magnets 22 to the related art lower frame 21 at fixed intervals leads to a complicated fabrication process. That is, the fastening of the magnets 22 to the jig and winding the back yoke 23 therearound for fitting the magnets 22 to the lower frame 21 requires many fabrication steps, that causes many defects, to increase a production cost.